1. Field of the Invention
This invention relates to antimicrobial hydroxyapatite powders, wherein metal ions having an antimicrobial property such as silver, copper and zinc ions, or organic antimicrobial agents such as hinokitiol, tannin, lysozyme, protamine and sorbic acid are included in hydroxyapatite powders having good affinity for a living body. These powders are widely used in the medical, dental and hygienic fields as artificial bone, artificial root of a tooth, dentifrice, dental cement, supplement for bone deficit and cosmetic materials.
2. Description of the Prior Art
Antimicrobial agents are widely used in the fields of drugs, medical instruments, cosmetics, foods, kichenwares, package materials, filters, clothings and miscellaneous goods. They are particularly useful in places where many people eat, drink, breathe or otherwise congregate.
Antimicrobial agents are classified into two groups, that is, the synthetic or natural inorganic group and the synthetic or natural organic group. In practice, the antimicrobial agents now used are the organic substances. Inorganic antimicrobial agents are not yet in use because the antimicrobial properties of the metals and salts thereof depend upon metal ions. As a result, they can be only used in aqueous solutions and have strong toxicity and defects relating to coloring and change of color. However, organic antimicrobial agents also have defects such as high volability, low heat resistance, coloring and high solubility for water and organic solvents. Thus their fields of use are also limited.
Accordingly, various proposals have been made to overcome the defects of organic antimicrobial agents. For example, combinations of hinokitiol with alum and calcium salt have been proposed to prevent the coloring of hinokitiol (Japanese Patent Publication 59-224677) or the salt and inclusion compound thereof are used (Japanese Patent Publication 61-108359).
Generally, materials to be used for a living body are disinfected by heating or treating with ethyleneoxide and are preserved in the disinfected state to prevent the breeding and adhesion of unwanted bacteria. But, the problem of disinfecting with ethyleneoxides is that the ethyleneoxides are retained in said materials and thus contaminate the materials. Also the materials are often used in treating localized bodily infections, and hence the possibility for breeding bacteria in the infections may be high.
If the composition of hydroxyapatite is substantially the same as the composition of living body bone, then it has good affinity for the living body and is superior as a body material. However, proteins, amino acids and other organic substances are easily absorbed in hydroxyapatite, so then bacteria are also easily absorbed and breed in hydroxyapatite. Accordingly, when hydroxyapatite is used as a living body material, it is necessary to consider the contamination of hydroxyapatite with bacteria. To solve the problem of contamination of hydroxyapatite, it has been proposed to use antimicrobial agents with hydroxyapatite. However, because the antimicrobial agents usually used are organic substances having low heat resistance and high solubility, the heat treatment of the agents is difficult. Thus the antimicrobial agents usually used are difficult to use as materials for the living body and medical instruments.
Even if the organic antimicrobial agents have high anticontamination properties, the use of such the agents must be limited because of unfavorable problems such as change in taste, smell and discoloration that may occur when added directly to foods.
When said agents are used as an impregnation substance by permeating or absorbing said agents in a substrate such as paper, cloth, and water absorbable polymers, the sublimating of said agents from the surface during drying will decrease their antimicrobial properties. Also when said impregnation substances are used, the antimicrobial agents will be volatized, dissolved and deposited from the surface of said substances and then unwanted harmful damage may occur. Accordingly, in view of stability and safety, the use and preservation of impregnation substances present difficult problems. When the organic antimicrobial agents are directly added to the films and compact resins, the antimicrobial properties may be lost by the decomposition and sublimation of the antimicrobial agents. It is difficult to process said agents without the loss of its antimicrobial properties.
Methods where inorganic and organic antimicrobial agents are absorbed in zeolite and the treatments thereof are known. However, the problem is that zeolite absorbs comparatively small amounts of the antimicrobial agent. When ceramics such as SiO.sub.2, CaCo.sub.3 and Ca.sub.3 (PO.sub.4).sub.3 are used in place of zeolite, the retention of antimicrobial agent in said ceramics is relatively small. When ceramics containing antimicrobial agents are added to products such as the cosmetics, resins, fibers, papers and filters to obtain an antimicrobial property, it is necessary to use large amounts of said ceramics to have a sufficient antimicrobial properties. However, then the quality of the product is decreased since it contains large amounts of said ceramics.